dodge 1500

Probably just make it run too rich or too lean.

The biggest risk is the check engine light, the ECM doesn't like outta spec engine parameters caused by modification without compensation. Post cat O2 controls (mostly) long term fuel trim. The pre-cat O2 does the short term trim. Remove the back pressure of the cat n the pre-cat O2 sensor will command rich in a vain attempt to restore what it thinks is programmed and acceptable levels of O2 in the exhaust., post cat roughly the same unless you can set it far enough away from the exhaust stream to stop caring about O2 in the exhaust. This will futz with engine operation not to mention reduced gas milage n excessive emissions. If you live in an exhaust sniffing society, you'll fail a state inspection unless you have the ECM reprogrammed, not to mention...it's illegal.